All Medicare Enrollment Periods — Summary
| Period | When | What You Can Do | Coverage Starts |
|---|---|---|---|
| Initial Enrollment Period (IEP) | 7 months around 65th birthday | Enroll in Parts A, B; join MA or Part D | Depends on when you enroll (see below) |
| Annual Open Enrollment (OEP) | Oct 15 – Dec 7 | Switch MA plans; switch to/from Original Medicare; change Part D | January 1 |
| MA Open Enrollment (MA-OEP) | Jan 1 – Mar 31 | Switch MA plans; drop MA for Original Medicare + Part D | First of following month |
| General Enrollment Period (GEP) | Jan 1 – Mar 31 | Enroll in Part A or B if you missed IEP and don't qualify for SEP | July 1 |
| Special Enrollment Period (SEP) | Triggered by qualifying events | Enroll in or change Medicare based on life event | Depends on SEP type |
Initial Enrollment Period (IEP)
The IEP is your first — and most important — enrollment window. It spans 7 months total:
- 3 months before your birthday month
- Your birthday month itself
- 3 months after your birthday month
When your coverage starts depends on when during this window you enroll:
| When You Enroll | Part B Coverage Starts |
|---|---|
| 1–3 months before birthday month | First day of birthday month |
| Your birthday month | First day of the month after you enroll |
| 1 month after birthday month | First day of the month after you enroll |
| 2 months after birthday month | 2 months after you enroll |
| 3 months after birthday month | 3 months after you enroll |
Annual Open Enrollment Period (OEP)
Dates: October 15 – December 7 each year. Coverage changes take effect January 1.
This is the main annual window for beneficiaries already enrolled in Medicare to make changes. During OEP you can:
- Switch from Original Medicare to a Medicare Advantage plan
- Switch from Medicare Advantage back to Original Medicare
- Switch from one Medicare Advantage plan to another
- Join, switch, or drop a Part D plan
Review your current plan's Annual Notice of Change (ANOC) each fall — it tells you how your plan's benefits and costs are changing for the next year. If your drugs are being moved to a higher tier or your doctor is leaving the network, the OEP is your chance to switch.
Medicare Advantage Open Enrollment Period (MA-OEP)
Dates: January 1 – March 31 each year. Coverage starts the first day of the month after you request the change.
If you're enrolled in a Medicare Advantage plan, you have one opportunity during the MA-OEP to:
- Switch to a different Medicare Advantage plan
- Drop Medicare Advantage and return to Original Medicare (and join a Part D plan)
Note: During MA-OEP, you cannot switch from Original Medicare to Medicare Advantage. That can only happen during the annual OEP (Oct 15–Dec 7) or a qualifying SEP.
General Enrollment Period (GEP)
Dates: January 1 – March 31. Coverage starts: July 1.
The GEP is a safety valve for people who missed their IEP and don't qualify for a Special Enrollment Period. If you enroll during the GEP, be aware:
- Coverage doesn't start until July 1 — leaving a gap if you missed your IEP
- Late enrollment penalties for Part B and/or Part D will apply permanently
Special Enrollment Periods (SEP)
SEPs allow you to enroll in or change Medicare outside normal windows when certain qualifying life events occur. Common SEP triggers:
Working Past 65 with Employer Coverage
If you or your spouse has active coverage through a current employer (at a company with 20+ employees), you can delay Part B without penalty. You have 8 months from when that coverage ends (or your employment ends, whichever comes first) to enroll in Part B under an SEP.
Other Common SEPs
- Moving out of your Medicare Advantage plan's service area
- Your plan loses its Medicare contract or stops serving your area
- Gaining or losing Medicaid eligibility
- Qualifying for Extra Help (Low Income Subsidy)
- Returning to the U.S. after living abroad
- Being released from incarceration
Late Enrollment Penalties
Part B Late Penalty
If you don't enroll in Part B when first eligible and you don't have a qualifying SEP reason, you'll pay a 10% penalty for each full 12-month period you delayed. This is added to your monthly Part B premium permanently.
Example: If you delayed Part B by 2 years, your premium surcharge is 20% — so instead of $185/month, you'd pay $222/month for life.
Part D Late Penalty
If you go 63+ consecutive days without creditable drug coverage after your Part D enrollment window, the penalty is 1% of the national base beneficiary premium per month you lacked coverage. This is permanently added to your monthly Part D premium.
Part A Late Penalty
If you have to pay a premium for Part A and you don't enroll on time, your premium is 10% higher for twice the number of years you delayed.
How to Sign Up for Medicare
There are three ways to enroll:
- Online: Visit SSA.gov/medicare to apply online — available 24/7, typically takes 10 minutes.
- By phone: Call Social Security at 1-800-772-1213 (TTY: 1-800-325-0778), Monday–Friday 8 a.m.–7 p.m.
- In person: Visit your local Social Security office. Find locations at SSA.gov.
Enrollment Checklist
- ☐ Confirm your eligibility (age 65 or qualifying condition)
- ☐ Determine if you have current employer coverage that qualifies for SEP
- ☐ Note your 7-month IEP window (3 months before birthday month)
- ☐ Decide: Original Medicare or Medicare Advantage?
- ☐ Enroll in Part A and Part B (online, phone, or in-person)
- ☐ Choose and enroll in a Part D plan (or MAPD)
- ☐ If choosing Original Medicare, shop for a Medigap plan during your guaranteed-issue window
- ☐ Set a reminder to review your plan each October 15–December 7